Swirling flows abound in nature and numerous engineering applications. Under conditions which are not completely understood, the swirling cores could undergo a sudden enlargement of their vortex core, leading to a ’vortex breakdown’. The physics of vortex breakdown and strategies to control it have been active areas of research for nearly half a century. There are many competing theories of vortex breakdown in the literature; broadly, these are surmised on similarities to flow separation, hydrodynamic instability or transition from a supercritical to a subcritical state. However, a rational criterion for vortex breakdown continues to be elusive. One of the most well known criteria in the literature is the one due to Brown and Lopez (1990) based on an inviscid vortex dynamics model which suggests that the helix angle of the velocity vector should enclose the helix angle of the vorticity vector. However it appears that this only suggests that the stream surface would diverge and not necessarily constitute a condition for breakdown. In this work, we propose a new criterion based on helicity (scalar product of velocity and vorticity vectors) for characterizing breakdown since it has fundamental topological interpretations relating to change in linkages of vortex lines. In particular, it is suggested that the breakdown location corresponds to the location where helicity becomes zero. We study the problem of vortex breakdown in a cylindrical container with a rotating top lid in order to clarify and elucidate our hypothesis. We present results from Direct Numerical Simulation of this problem for three different Reynolds numbers and evaluate the utility of our proposed helicity criterion. Our studies indicate that helicity is indeed a better choice for characterizing vortex breakdown.

No description available.

Degrowth is an emerging field of research and a social movement founded on the premise that perpetual economic growth is incompatible with the biophysical limits of our finite planet (D’Alisa, Demaria & Kallis, 2014a; Asara, Otero, Demaria & Corbera, 2015). Despite the important work that degrowth scholars and activists have done to broadcast the fundamental contradiction between endless compound growth and a finite resource base, degrowth remains politically marginal, having received little mainstream attention or policy uptake. This thesis explores why. In particular, I examine barriers to and pathways towards the uptake of degrowth in Canada, a country that disproportionately contributes to climate breakdown. To do so I ask: 1) What barriers exist to advancing a degrowth agenda in Canada?; 2) How specifically do those barriers block degrowth from taking hold in contemporary Canadian policy and political discourse?; 3) How (if at all) are Canadian activists seeking to address these barriers? This research reveals that the political economy in Canada, and the way that is expressed in concentrations of elite and corporate power has given certain actors, particularly the fossil fuel industry, immense economic and political power. These concentrations of power, and the ways they are maintained reinforce a politics and discourse that is highly antithetical to the politics of degrowth, and thus serve as a major barrier to the emergence of degrowth. I argue, in order to move towards a degrowth politics, the hegemony of fossil capitalism in Canada, and the specific class interests that support it needs to be challenged. While degrowth has a strong critique of economic growth and capitalism, this alone is not enough. Any movement towards degrowth will require transforming power relations. This means continuing to explore the concrete ways specific institutions continue to create the political economic conditions that support fossil fueled growth as its main priority, and prioritizing building broad based movements to counter them. / Graduate

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering, 2016 / The validity of the atmospheric correction method presented in the IEC 60060-1 (2010) standard is analysed and evaluated by means of theoretical and laboratory work. In order to understand the problem, the evolution of the atmospheric correction methods, from as early as 1914, has been presented. A procedure (Calva prediction method) for predicting the direct current (DC) breakdown voltage for an air gap at any altitude was discovered and was also analysed along with the IEC 60060-1 (2010). A critique of some of the atmospheric correction methods commonly used standards was also done. Experiments were carried out at altitudes of 1 740 m (Wits University), 130 m (UKZN HVDC centre) and at less than 2 m above sea level (Scottburgh beach, Clansthal). More tests were conducted using a pressure vessel where high altitude relative air density was simulated. All tests were conducted on rod-plane air gaps using a 15 mm diameter at tip rod. Test results from Scottburgh beach were used as the standard breakdown voltages of the air gaps tested since the environmental conditions were the closest to the conventional standard conditions (stp). The test results obtained were compared with predictions using the Calva method in order to validate the method. The test results were also corrected according to IEC 60060-1 (2010) and compared to the standard breakdown voltages obtained at Scottburgh beach. It was shown that the IEC 60060-1 (2010) is quite suitable for atmospheric correction for data obtained at low altitudes (about 130 m). When applied to high altitude (1 740 m) data, the correction method is accurate and suitable for very small air gaps less than 0.1 m. As the air gap length increased, the corrected results began to deviate from the expected standard voltage. The same trend was shown with the corrected results from the pressure chamber tests. The prediction method by Calva was accurate when compared to the experimental data from the high altitude and low altitude test results. When compared to the data from the pressure chamber, the prediction method had a linear error factor which was di erent for each gap length. It was concluded that the IEC 60060-1 (2010) is not only unsuitable for atmospheric correction for data at relative air densities below 0.8, but also that the correction method is prone to an increase in error as the air gap length increases when the relative air density is higher than 0.8. The Calva prediction method was found to be suitable to use after additional factors are added when applied to high altitude conditions. / GR2016

Nuclear plant stainless steel can become contaminated by radionuclides during normal operation whereby the final disposition of these materials then becomes a major decommissioning challenge to address. Characterisation of the chemical and metallurgical processes that underpin contamination is essential in consideration of developing cost effective decontamination and prevention methods, as are in situ measurement techniques that allow assessment of contamination. To address these issues, contamination experiments to simulate the nitric acid-based reprocessing streams of the PUREX (Plutonium Uranium Redox Extraction) process, and alkaline spent fuel storage ponds were investigated. Solution and surface spectroscopic measurements were performed to characterise the sorption behaviour of stable analogues of two high yield fission products, Sr-90 and Cs-137, on as received and 30 % cold rolled AISI Type 304 stainless steel, respectively. In addition Laser Induced Breakdown Spectroscopy (LIBS) was also investigated as a standoff contamination assessment technique. Fission product accumulation was modelled to a second order kinetic fit that considers chemisorption, typically to a hydrous metal oxide surface, as rate controlling. This process is observed to be independent of solution composition and strain processing regime. This behaviour reflects complexation to the passivating surface chromium oxide film, and as determined by depth elemental analysis, effectively inhibits contaminant migration into the bulk material. Environment chemistry and microstructural variables that destabilise the Cr-rich passive film however reduces the passive layer capabilities to effectively inhibit fission product bulk diffusion. The importance of corrosion phenomena towards radionuclide sorption processes necessitates the consideration of metallurgical and chemical factors during the implementation of decontamination approaches to treat affected plant material at nuclear licenced sites. LIBS was found to be a satisfactory technique for measurement of Sr sorbed to steel but Cs could not be detected at the concentrations used in this experimentation. Furthermore, EDX and TOF-SIMS elemental mapping indicated ablated material may be redistributed into the crater profile during elemental analysis. This process has clear implications for the deployment of LIBS for in situ characterisation of nuclear materials as the uncontrolled redistribution of radioactive material certainly violates decommissioning principles.

No description available.

This dissertation outlines the study and development of a Solid-state Impact-ionization Multiplier (SIM). The SIM is a stand-alone current amplifier designed with optical detection systems in mind. The SIM amplifies signals utilizing impact ionization as a source of gain. The SIM is fabricated on silicon in order to take advantage of its favorable impact ionization coefficients. Utilizing silicon in impact ionization based gain devices makes low noise and high gains attainable. Because it is a stand-alone device, it can be wired to an arbitrary current source making it capable of receiving an input from photodiodes of any material. This makes it possible to amplify a signal from a photodiode that has been optimized for a given wavelength. In this way, the SIM attempts to separate the absorption and multiplication portions in modern day optical detection/amplification devices such as in Avalanche Photodiodes (APDs). This flexibility allows it to be utilized in many different systems. The SIM has gone through several iterations in the last few years. Each change has been with the purpose of increasing gain, frequency response or yield. The progression of the device has come at the hand of much thought, theory, simulation, fabrication, and testing. One of the challenges encountered in its development has been gain controllability due to poor carrier confinement and premature breakdown. Increased gain control was developed through simulation and fabrication of a confining oxide layer. Yield and difficulties in consistent fabrication were also addressed by altering the input metallization and doping processes. The frequency response of the device has been the largest challenge in device development. Issues such as space charge, floating node voltage, edge effects and low signal amplification have caused limitations. Successes and attempts at overcoming these, and other, challenges is the basis of this dissertation of work.

Electrical insulation under high voltage can eventually fail, causing critical damage to electronics. Such electrostatic discharge (ESD) is the primary source of anomalies or failures on spacecraft due to charged particles from the Sun or planetary radiation belts accumulating in spacecraft insulators. Highvoltage direct current power distribution is another example of a growing industry that needs to estimate the operational lifetime of electrical insulation. My research compares laboratory tests of ESD events in common insulating materials to a physics-based model of breakdown. This model of breakdown is based on the approximation that there are two primary types of defects in structurally amorphous insulators. One of the two defect modes can switch on and off depending on the material temperature. This dual-defect model can be used to explain both ESD and less-destructive transient partial discharges. I show that the results of ESD tests agree reasonably well with the dual defect model. I also show that transient partial discharges, which are usually ignored during ESD tests, are closely related to the probability of catastrophic ESD occurring. Since many partial discharges are typically seen during one ESD test, this relationship suggests that the measurements of partial discharges could accelerate the testing needed to characterize the likelihood of ESD in insulating materials.

Conflict in marital relationships affects couple intimacy and satisfaction impacting on the couple system, the family system and wider social systems. Negative conflict is associated with breakdown in intimacy, marital dissatisfaction, and is seen to be a prominent cause of marital failure. As conflict is a process, it has the possibility of change and development over time, including moving towards a process whereby disagreements can be worked out with mutually acceptable solutions. Theoretical frameworks for conflict and marital counselling were reviewed and the systems-interactionist theory and a systemic-based counselling approach chosen for the purposes of this study. It was hypothesised that a systemic-based counselling approach would lower the levels of conflict occurring within a marital relationship. The principal objective of this study was to provide a more rigorous investigation than previous studies of client perceptions of the effectiveness of a systems-based counselling approach for marital counselling. Three case studies were conducted, with embedded units of analysis, within the context of a therapeutic process which drew on current theories of systemic counselling. Conflict was measured and operationalised as overt behavioural conflict, communication of negative affect, frequency of disagreements, intensity of disagreements, desire to change the other partner, the desire for change, and evidence of, and frequency of, positive conflict. As the study was based on the client's perceptions of change, multi-methods of selfreports were employed. As none of the known measurements met the needs of this study, a questionnaire known as the QCR was devised specifically for the pre- and posttests. The QCR was designed to measure: any increase or decrease in positive conflict; changes to both the intensity and frequency in negative conflict; and perceptions of the desire for change. The effectiveness of the counselling approach was measured by comparing the results of the pre-and post-tests with the continual self-reports and the self-reports at the long term follow-up interviews. An analysis of the self-reports focus on: the desire for change; the effectiveness of a systems based counselling approach in lowering negative conflict; and the usefulness of the QCR and other tools as measures. The systems-based-counselling approach, proved from the clients' perspective, to be: highly effective in case one; mostly effective in case two; and ineffective in case three as one partner aborted the counselling process. The systems-based-counselling approach had variable success in decreasing the intensity of negative conflict but was mostly successful in decreasing the frequency of negative conflict. This approach was not largely successful in reporting an increase in the frequency of positive conflict. The study revealed evidence of a relationship between commitment to the marital relationship and negative conflict. It also adds to the debate about the appropriateness of a systems-based counselling approach in violent relationships. In judging the clients' perceptions of the effectiveness of the systems-based counselling approach multi-measurements employed including the lengthy recording of the therapeutic sessions. It is claimed that this thesis offers a more rigorous methodology than anecdotal evidence previously used in the reporting of systemic counselling cases.

Jay W. Lathrop, Sanborn C. Brown. / "December 1, 1949." / Army Signal Corps Contract No. W-36-039 sc-32037 Project No. 102B. Dept. of the Army Project No. 3-99-10-022.